This invention relates to blenders and more particularly to method and apparatus for thoroughly blending particulate or granular materials.
As storage bins or hoppers are filled with granular or particulate material, it often happens that an inhomogeneous distribution of material occurs. There may be several reasons for this result. In the first place, as material flows into a hopper, the material beneath the inlet nozzle piles up at the so-called angle of repose of the material. In this case the larger particles often roll down the peak toward the sides of the hopper, leaving the finer particles in the central region. Inhomogeneity can also occur when the hopper is filled with different batches of the same material because of variations in composition of individual batches. When material is drawn off through an outlet at the bottom of the hopper, the material flows from the region directly above the nozzle. Thus, the material which is drawn from the hopper as needed will not be representative of the average characteristics of the material in the hopper.
Prior art attempts at a solution to this segregation problem typically included placing a perforated blending tube within the hopper. Such a tube has openings spaced apart along its axis which allow material from all levels within the hopper to enter the tube. The lower portion of the blending tube communicates with the outlet nozzle so that a more nearly homogeneous mixture of the material issues from the outlet of the hopper. Another known blending apparatus includes cylindrical weirs whose heights decrease from the center of the hopper outwardly. In such a device the discharge nozzle communicates with each of the segments created by the cylindrical weirs so that material is sampled from various radial positions within the hopper. Although the known apparatus discharges a more nearly homogenous mixture of the granular material than would be the case with a simple hopper with a bottom outlet, there is room for considerable improvement in the mixing capabilities of storage bins.
It is an object of the invention, therefore, to provide method and apparatus for effecting a more thorough mixing of particulate material as it discharges from a hopper.
It is a further object to provide such apparatus which is simple of construction and inexpensive to use and maintain.
It is a still further object of the invention to provide apparatus for effective blending of very large lots of particulate material.